Diving beetles (Dytiscidae) as predators of mosquito larvae (Culicidae) in field experiments and in laboratory tests of prey preference

Abstract

Field experiments were performed in artificial ponds to evaluate how the density of predatory diving beetles (Dytiscidae) would affect the population levels of mosquito larvae (Culicidae). Mosquitoes colonizing the ponds were predominantly species of the genus Culex. In 2000, most of the dytiscids colonizing the ponds were small (Hydroporus spp.), and these predators had no impact on the size of larval mosquito populations, not even in ponds with added dytiscids. In 2001, larger beetles (Ilybius, Rhantus, and Agabus spp.) were more common, and there were significantly fewer mosquito larvae in ponds with the highest numbers of dytiscids. There was a negative correlation between numbers of diving beetles in the ponds and the mean body length of mosquito larvae. In neither year could dytiscid densities be maintained above a certain level owing to emigration. In laboratory tests, there were marked differences between three common dytiscid species in regard to preferences for Daphnia and Culex species as prey: Colymbetes paykulli Erichson chose mosquito larvae more often, whereas both Ilybius ater (De Geer) and I. fuliginosus (Fabricius) preferred Daphnia spp. All of the tested dytiscids consumed large numbers of prey. Since some dytiscid species can efficiently decrease populations of mosquito larvae, they are probably important in the natural control of these dipterans.

Diving beetle assemblages of flooded wetlands in relation to time, wetland type and Bti-based mosquito control

“…Dytiscids and some aquatic Hemiptera as generalist predators have been claimed as predators on mosquito larvae (Nilsson & Svensson, 1994;Blaustein, 1998;Lundkvist et al, 2003;Medlock & Snow, 2008), but no direct Bti-effect is known on these orders (Boisvert & Boisvert, 2000). In our analyses, Bti against mosquito larvae seemed to play only a minor role in structuring the dytiscid species assemblage, and the only significant result was a possible positive effect on the medium-sized dytiscids.…”

“…In fact, Deding (1988) found Chironomidae and small crustaceans to dominate as recognizable food items for the majority of the dytiscid species studied. Lundkvist et al (2003) found different prey preference of three medium-sized dytiscid species on two alternative preys (mosquito larvae and Daphnia) in laboratory tests. Flood water mosquito larvae may constitute an example of an unpredictable super-abundant food resource that varies strongly within and between years.…”

“…As generalist predators, dytiscids may feed on all available prey taxa and mosquito larvae will be only one prey among others however super-abundant. Many dytiscids are known to include mosquito larvae in their diet (Deding, 1988;Nilsson & Söderström, 1988;Nilsson & Svensson, 1994;Lundkvist et al, 2003;Medlock & Snow, 2008), and a few studies show that dytiscids may lower the mosquito larvae abundance in lab and in the field (Lundkvist et al, 2003;Aditya et al, 2006;Chandra et al, 2008).…”

“…The three dytiscid size-classes were small (2-6.9 mm), medium-sized (7-15.9 mm) and large (≥16 mm) and followed the size distribution of dytiscid species in Nilsson & Holmen (1995). Moreover, species in all three size-classes have been observed to be predators on mosquito larvae (Nilsson & Söderström, 1988;Nilsson & Holmen, 1995;Lundkvist et al, 2003). Number of individuals in all three size classes was McQuitty Similarity analysis range from zero and upwards, depending on the similarities in the groups defined.…”

“…Dytiscids are generalist aquatic predators that will feed on any suitable aquatic prey, however food preference seem to occur for at least some species (Deding, 1988;Kehl & Dettner, 2003;Lundkvist et al, 2003).…”